1. Field of the Invention
The present invention relates to an optical scanning device and an image forming apparatus, more specifically to an optical scanning device which scans scan target surfaces with light and an image forming apparatus including the optical scanning device.
2. Description of the Related Art
In the field of electrophotographic image recording, an image forming apparatus using a laser is widely used. The image forming apparatus includes, for example, a photosensitive drum (hereinafter also referred to as the photoconductor drum) and an optical scanning device which forms a latent image on an outer circumferential surface of the photoconductor drum. The optical scanning device includes, for example, a light source which emits laser light, an optical deflector, such as a polygon mirror, for example, which deflects the laser light emitted from the light source, and a optical scanning system which collects the laser light deflected by the optical deflector onto the outer circumferential surface of the photoconductor drum.
In recent years, along with the colorization of images and the increase in processing speed of image forming apparatuses, a tandem-type image forming apparatus including a plurality of photosensitive drums (normally four) has been increasingly used.
The tandem-type image forming apparatus tends to be increased in size in accordance with the increase in the number of photoconductor drums. Therefore, there is demand for a reduction in device size, including a reduction in size of the optical scanning device. To reduce the size of the optical scanning device, it is effective to cause optical paths of a plurality of laser lights directed from the optical deflector toward the respective photoconductor drums to overlap one another.
For example, a recording device may include two laser light sources, a polarized light combining device, a deflection device, and a polarized light separating device. The two laser light sources radiate two laser lights linearly polarized in mutually perpendicular directions and modulated in brightness in accordance with signals to be recorded. The polarized light combining device combines the two laser lights radiated from the laser light sources. The deflection device deflects a resultant synthesized laser light in a main scanning direction. The polarized light separating device causes the synthesized laser light deflected by the deflection device to be separated and strike different spots on a surface to be scanned for recording.
Further, the optical scanning device may include a single laser light source, an information control device, a polarization control device, a scanning device, a separation device, and an optical rotation control device. The information control device provides mutually different information items to two polarized lights of a laser light emitted from the light source. The polarization control device controls the polarization amount on the basis of the information received from the information control device. The scanning device scans and irradiates a predetermined irradiation surface with the polarization-controlled light. The separation device separates the scanning light into two lights in accordance with the polarization state. The optical rotation control device performs an optical rotation control on the laser light in accordance with the angle of incidence of the light incident on the separation device from the scanning device.
Further, the optical scanning device may include a polarization separation device which causes a first light having a first polarization direction and a second light having a second polarization direction to be separated from each other.
The above-described devices, however, have difficulty in stably suppressing the generation of ghost light, i.e., optical noise, without causing an increase in cost and device size.